Vascular stents are being used clinically in increasing numbers for a variety of vascular disorders, but thrombosis and neointimal hyperplasia continue to compromise the potential utility of these devices. The research outlined in this proposal is based on the hypothesis that fluid mechanical phenomenon are, in part, responsible for clinical failures of vascular stents. The overall goals of this research are to determine how fluid mechanics may be related to platelet deposition on stents in the acute implementation stage, and how stent design can be changed to minimize the risk of flow-related restonosis. The specific aims of the proposed research are: Determine the amount of overall platelet deposition in cylindrical compliant stented artery models using an in vitro flow apparatus with human blood as the working fluid. Platelet deposition will be quantified by the present of radioactively labeled platelets on the tube wall. Three different stent designs (two commercially available designs and one prototype design) will be studied. Determine the localization of platelet deposition in a flate-plate stented artery model using fluorescent labeled platelets and confocal microscopy. The same three stent designs will be studied. Quantify the degree of flow separation and stagnation in the three different stent designs using computational fluid dynamics (CFD) techniques. Since the presence of pulsatile flow burs the definition of flow separation, a separation parameter has been defined and will be varied parametrically. Areas of flow stagnation will be identified by the presence of persistent low all shear rates. The extent of flow separation and stagnation will be statistically compared with the platelet deposition data. Further elucidate the role of flow patterns in platelet deposition in stents by performing experimental and computational particle tracking. Particle residence times will be quantified near the struts of the same three stent designs and statistically compared with the platelet deposition data. Stimulate the progression of neointimal development in the CFD flow simulations by "filling in" areas of flow separation. The separation parameter mention above will be adapted to define areas of pulsatile flow separation. The resulting tissue growth patterns will be compared with available in vivo data on neointimal development patterns. This work is expected to provide unique information on the mechanical aspects of stenting. This information will aid in developing the next generation of stent design in which arterial mechanics are a prime consideration.